How To Determine Amount Of Water Needed To Brew

When I first started with all grain, I ended up knocking my head against the wall trying to determine the amount of water needed to mash…

…of course this wasn’t much of a problem for steeping grains, but then again I wasn’t doing it right either…

With extract brewing, there is a simple rule of thumb to follow… ‘boil big, steep small’… but with all grain brewing, boiling big is not always what you want and mashing has to be a little more precise than just ‘small’…

So we’ll get steeping out of the way and just go with proven ratio of using less than one gallon of water per pound of grains… and this is just a rule of thumb, because really what you are trying to accomplish by keeping the ratio this way is you pH levels below 6 among other things…

Now, the amount needed for all-grain is a whole different animal altogether…

Grain Absorption
First we have to account for the amount of water the grains will soak up during the mash, which can not be drained in the lauter tun… this usually is about .1 to .18 of the initial weight of the grain… so if you mash 10 lbs of grain, you will lose about 1 to 1.8 gallons of water to the grains…

In my system this is about 1.36 gallons, but you don’t need to be that precise…

Lauter Tun Water Loss
Depending on the configuration of your false bottom, there may be water left in the lauter tun that you were not able to drain, but was not absorbed by the grains…

My system drains the wort to within 1/8″ from the botton of the lauter tun so I only loose just under two cups of wort… to find out yours, you’ll have to remove the grains from your

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  • Jeff

    Reply Reply March 28, 2011

    Great info. I like using a constant and just worrying about the loss of water during the mash. How do you determine the boiloff rate?

  • William

    Reply Reply March 28, 2011

    This seems a little complicated, and that’s why I use brewing software.

  • Jorge

    Reply Reply March 28, 2011

    @Jeff – That depends on your system and how fast your wort evaporates during the boil as well as how long you boil for… if you start with 6 gallons and you end up with 5.5 gallons after one hour, then you simply divide 5.5 by 6 and you get .92… that means your boil off rate is 8% per hour.

    @William – I hear you… that’s how I determine it nowadays, but I used this 2 step technique for quite a while…

  • Jason

    Reply Reply March 28, 2011

    How did you determine that your system loses 1.36 gallons in the mash?

  • Frank

    Reply Reply March 8, 2012

    I think your math is a little off..”That means you need to add the 5% you would lose to evaporation and that is done by dividing 6.75 by 95%… so you would get about 7.11 gallons of water you need…” – Since we are assuming 6.75 gallons is what we put into the mash, with 1.75 gallons lost – we’d have 5.00 gallons in our kettle. So the math to account for evaporation should be based on 5.00 gallons and not 6.75 gallons as you’ve indicated. If we want to end up with 5.00 gallons after the boil, with 5% evaporation rate (disregarding shrinkage), then we need to start with 5.26 gallons (5.00/0.95); this means an addition 0.26 gallons of water is needed in addition to the 1.75 lost in the mash. This comes out to 7.01 gallons (1.75 + 0.26 + 5.00) total water needed

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